Conventional vinyl wall covering products, whether calendered, extruded or plastisol coated, act like a vapor barrier when applied to a wall. For many applications such as, for example, bathrooms and kitchens, this is a desirable feature. In bathrooms, the moisture collects on the outside of the wall covering exposed to the room, whereas paper wall coverings would become saturated and soggy. In kitchens or other areas where splattering or marks require frequent washing, again a moisture barrier wall covering is desired.
However, certain applications would benefit from porous, semiporous, semipermeable, also called breathable, wall covering products. One particular circumstance in which moisture barrier wall coverings are not desired is homes, hotels, motels, offices and commercial decorating in geographic regions of very high humidity, such as the Southern United States. The high moisture level in the air permeates the walls from the exterior inwardly resulting in condensation on the outside surface of vinyl wall coverings of rooms cooled by air conditioning. As a result, the condensate collects on the back or exterior side of the cooled, vapor barrier wall covering and causes mold, mildew, and other degradation processes and fungi growth on or within the wall. These adverse reactions to the high humidity accelerate the failure of the wall covering product, degradation or destruction of the wall beneath, noticeable and offensive odors, all at great expense to owners of, for example, large commercial buildings in these geographic regions. Mold, mildew and musty odors cost the American hotel and motel industry over $70 million every year in lost revenue and repair costs.
Mold and mildew are fungi and over 90% of them have airborne spores. Fungal growth requires four elements: spores, temperature, food and moisture. Stopping mildew growth requires elimination of one or more of these essential elements. As a practical matter, spores are always present and virtually impossible to eliminate in most buildings. Temperature ideal for fungal growth is always available in buildings since mold and mildew prefer the range of temperatures comfortable to humans. Fungal nutrients are always available in some form since fungi can feed on virtually any organic material. Thus, removing moisture is the most practical method of controlling fungal growth.
The amount of moisture needed to support fungal growth depends on the type of material available as a food source. For instance, wall paper pastes based on corn starch or wheat starch with a moisture content above 15% of its dry weight becomes a very favorable environment for mold growth. In contrast, most types of wallboard must absorb over 30% of their dry weight in water before they will support mold growth. Relative humidities of 50% to 75% or above are frequently seen in, for example, southeastern United States.
It would therefore be desirable to have a strong and breathable plastic wall covering product which eliminates condensation and trapped moisture and allows the penetration of exterior humid air through the wall covering and into a room where the moist air can be dehumidified by the dehumidifier and/or air conditioner.